The present invention relates to a test mark which is provided on a connection for interconnecting at least two of a panel substrate, TAB tape, and flexible board of a display panel to easily check for any defect in the connection, and also relates to an electronic device with a display panel, a TAB tape, or a flexible board which are provided with this test mark thereon.
The present application claims priority from Japanese Application No. 2002-42558, the disclosure of which is incorporated herein by reference for all purposes.
As portable telephones and portable digital assistants (PDAs) have become widely available, small and thin display panels with a high display capability have been increasingly demanded. Liquid crystal display panels or organic EL (electroluminescent) display panels have been employed as the display panel which meet the demand.
To improve the display capability of such a display panel, it is critical to mount electronic components with high accuracy on the display panel as well as to improve the optical controllability and light-emitting property of each display element.
Referring now to FIG. 9, a process for mounting electronic components on the aforementioned display panel is described below. By way of example, among the electronic components which are connected to the display panel, such as a TAB (Tape Automated Bonding) tape or FPC (Flexible Printed Circuit) board, described in this embodiment is the TAB tape to be connected to the display panel.
A panel substrate 51 of a display panel 50 has leads 51a extending from the display panel 50 to an end portion thereof. Leads 52a of a TAB tape 52 are connected to the leads 51a via an ACF (Anisotropic Conductive Film) 53. There are provided alignment marks 51b on both the right and left sides of the connection area formed by the leads 51a of the panel substrate 51. Image pickup devices 54 are used to monitor the alignment marks 51b and alignment marks 52b on the TAB tape 52 which are aligned therewith. The monitored images are observed or subjected to image processing to align the TAB tape 52 with the display panel 50 by means of an alignment mechanism (not shown) in a manner such that they are positioned in place.
After the alignment has been completed, the end portion of the panel substrate 51 and the end portion of the TAB tape 52 overlap each other with the ACF 53 being sandwiched therebetween. With this arrangement, a pre-attach pressure head 55 is pushed against the overlap to press and pre-attach the TAB tape 52 to the panel substrate 51 via the ACF 53.
After this pressure pre-attachment has been completed, the alignment marks are checked for any misalignment, and the end portions are checked for any dust particles as well. Then, only those panels which have passed these checks are sent to the subsequent process. In the process for final attachment by pressure, the pressure pre-attached portion is subjected to a predetermined temperature and a predetermined pressure for a predetermined period of time, so as to completely attach the TAB tape 52 to the panel substrate 51 by pressure.
However, it is still difficult to perfectly align the very closely spaced leads with each other even through the alignment using the aforementioned alignment marks because of a lack in resolution of the picked-up images or individual errors in the substrate glass, TAB tape, and FPC caused when they are formed. Additionally, in the pressure pre-attachment or the final pressure attachment process after alignment, dislocation or defective pressure attachment may occur to result in defective connection.
In particular, for a display panel such as an organic EL display panel including current injection display elements, even a slight dislocation may decrease the contact area between the interconnected leads, hence bringing about an adverse effect on the injection current. The decrease in contact area between the leads (even they are securely connected to each other) can degrade display performance. Accordingly, more precise alignment is required than by the voltage-driven liquid crystal display panel. In this context, for the organic EL display panel, at the first stage, panel substrates with TAB tapes having been pressure attached thereto are visually inspected and then rejected if they are so badly misaligned that their misalignment can be recognized visually. Then, the remaining panels are checked using a microscope to see if a proper contact area is left between every two mutually contacted leads.
Since the visual inspection using a microscope is a troublesome hard-load operation, it is therefore desired to check panels as small in number as possible using the microscope and thus reject as many panels as possible in the preceding visual inspection process. However, it is impossible to know thoroughly by the visual inspection whether the contact area is properly left between the leads. Additionally, the aforementioned alignment marks for alignment are too small to be used for the visual inspection to check for misalignment. As a result, only such obvious defectives as caused by the pressure attachment are removed in the visual inspection process, hence rendering the microscope inspection to remain unchanged.